How to close the connection pool without shutting down the JVM while there are connections being used?

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Description

Suppose there are several connections being used now by different servlets. calling the basicDataSource,close() does not have any impact on the connection pool. I expect that after these servlet return the connections the pool should be shut down immediately. I also expect that any more requests to borrow connections from the pool should not be fulfilled. However, my experiment does not seem to support my expectations. Calling basicDataSource.close() seems to be ignored while there are connections being used.